1. Field of the Invention
This invention relates to a rule for regulating an action mechanism in a grand piano.
2. Description of the Prior Art
In general, a piano is constructed so as to produce a sound by striking a wire, which is provided in a tensed state on a frame, with a hammer via an action mechanism in accordance with a key pressing operation. One action mechanism is provided correspondingly to one key. In order to normally operate an action mechanism in accordance with the pressing of the relative key and strike the wire with the hammer, an operation called "regulation" in which each action mechanism is regulated is necessarily carried out. This operation includes:
(1) Regulation of a hammer stroke for setting a distance between a hammer and a wire in a non-operating condition.
(2) Regulation of the starting of a damper for setting the time of starting the production of a sound at which a damper relative to a pressed key leaves a wire, and the time of ending the production of the sound at which the damper holds the wire.
(3) Regulation of hammer let-off in which a hammer is moved back from a position short of a wire when a key is pressed gently.
(4) Regulation of a hammer back stop for setting the position occupied by a hammer when a jack in an action mechanism returns, in such a manner that the hammer can strike repeatedly without trouble.
In all of these regulating operations, preset specified quantities based on the relating of relative positions of a hammer and the lower surface of a wire are provided. Since these regulating operations require perception and experience, they are carried out by a skilled technician called a tuner.
In order to carry out these regulating operations easily, a substantially E-shaped stroke rule V consisting of a metal material, such as a thick iron plate and shown in FIG. 4 is used. In this stroke rule V, the distances a, b, and c are set to the quantities of hammer stroke, hammer back stop and hammer let-off respectively. In order to regulate the quantity a of hammer stroke, the stroke rule V is placed so that the upper surface of a second member V.sub.2 thereof and the lower surface of a first member V.sub.3 thereof contact the lower surfaces of wires S and the upper end surface of a hammer H respectively as shown in FIG. 5. In order to regulate a hammer back stop, the stroke rule V is placed so that the first member V.sub.3 is held between the lower surfaces of the wires S and the upper end surface of the hammer H so as to set the distance between these surfaces equal to the quantity b of hammer back stop. In order to regulate the hammer let-off, the stroke rule V is placed so that a third member V.sub.1 thereof is held between the lower surfaces of the wire S and the upper end surface of the hammer H so as to attain the quantity c of hammer let-off. The action mechanism is thus regulated in accordance with the objects of the regulating operations.
Since the stroke rule V of this construction has specified quantities set thereon in accordance with each regulating operation, the action mechanism may be regulated so that these specified quantities are attained. However, in order to carry out a regulating operation, the stroke rule V cannot be placed on or fixed to the upper surfaces of the wires S, neither can the heavy rule be placed on the upper surface of a hammer in operation. Therefore, it is necessary that a tuner carries out measurement and the regulation of an action mechanism as he holds the rule in one hand and brings it into contact with the lower surfaces of the wires with a tool held in the other hand. This makes it difficult to carry out a regulating operation, and requires much time to carry out the same.
Since the rule is formed so that different specified quantities are determined by different portions thereof, the measuring portions of the rule have to be changed by moving the rule every time each measuring and regulating operation in the same-pitched sound section has been completed, and the rule has to be inserted between and removed from the wires S and hammer H each time. Namely, each measuring and regulating operation cannot be carried out by setting the rule once.
In the low-pitched sound section, a damper D is positioned just above the relative hammer H. Therefore, the damper obstructs the insertion of the stroke rule, so that a stroke rule setting operation and an action mechanism regulating operation becomes difficult and inaccurate respectively. Whenever there is a difference between a distance between a hammer not yet regulated and the relative wire and each specified quantity of the stroke rule, the quantity of the difference is measured with the eye. Consequently, an accurate quantity of the difference cannot be determined, and an accurate regulating operation depends upon the tuner's perception and experience.